Mechanical characteristics and multiscale modeling for colloidal magnetorheological fluids at high shear rates

Colloidal magnetorheological fluid (CMRF) represents a novel magneto-sensitive smart material, which has the characteristics of high magneto-induced yield stress and non-settlement. The properties offered CMRF the ability to dissipate energy in an extremely short time, providing new ideas for intelligent energy absorption in high-speed crash and shock applications. High shear motion causes an increase in the Reynolds number, resulting in unpredictable rheological behavior. Therefore, it is necessary to explore the magneto-mechanical coupling characteristic of CMRF in high shear rates and magnetic fields. To address the question, this work designed a coaxial cylindrical rheological testing device, which shear rate can achieve about 4.0 × 104 s−1. A series of experiments based on the testing device for polyurethane-based CMRF with different mass fractions and cross-linking degrees were carried out. An interesting phenomenon called “platform effect” was found, in which shear stress showed a trend of first rising, flatting, and slightly declining. To explain the magneto-mechanical coupling mechanism of the “platform effect” for CMRF, a multiscale model was established by combining the magnetic dipole theory and mathematical statistics method. The average error of shear stress between the experimental test and theory calculation is only 10.04%, which shows the model can explain the experimental phenomenon.